Portable personal computers have developed from early luggable "suit case" designs, through the smaller "laptop" design, and now, with the aid of increasingly smaller packaging to "notebook," "sub-notebook" and personal digital assistants (PDAs) such as pen computers. While early portables were bulky and inefficient, laptops, notebooks and personal digital assistants have considerably improved the state-of-the-art by providing a battery supply, light weight circuitry and computer storage devices in a compact housing that can easily be carried by the user. As development of portable personal computers has advanced, substantially the full function of a more conventional desktop machine has been retained in the larger model such as the notebooks, while the subnotebooks typically lack floppy disk drives and the PDAs also typically lack keyboards due to their small size.
A "notebook" personal computer is about the size of a conventional loose leaf binder holding letter size paper, and typically weighs about 5-8 pounds. PDAs typically are too small to incorporate a keyboard and therefore often use a pen as the main interface for input. PDAs may weigh less than one pound to about 3 pounds with a screen size of about 5 by 7 inches or smaller. Those portable computers having size, weight and performance lying between the notebook and PDA are typically referred to as subnotebooks. In many portable notebook computer models, a keyboard compartment is hinged to a display screen compartment in such a manner that it is possible to fold the display screen compartment down against the keyboard compartment and to latch the two together. PDAs typically are a single enclosure with a screen on the top surface.
A limitation on the reduction in the size of personal computers has been the desire of users for a keyboard at least approximating those known and used with desktop and floor standing machines. Such conventional keyboards typically have an elongated rectangular form with alphanumeric keys arrayed in rows and staggered columns and with special function keys appropriate to the personal computer arrayed around the alphanumeric keys in a standard array. Such keyboards may have varying numbers and arrangements of keys, and several such arrangements have become more or less conventional and known by the number of keys provided. As efforts have been expended toward reducing the physical size of portable personal computers, some designers have chosen to reduce the size of the keys and thus the keyboards, while others have chosen to eliminate or combine certain functions provided in more conventional keyboards. Such efforts have succeeded to the point that notebook portable personal computers have had some success in the marketplace, however users of such computers often have complaints about key size and keyboard arrangement as compared with more conventional keyboards used with desktop machines. Restraints on key size and arrangement have effectively imposed a lower size limitation on keyboard length and width of about the size of a sheet of correspondence stationery. Moreover, because the alphanumeric keys must be of sufficient size to accommodate even large fingers, certain keys are often deleted or rearranged from their "usual" position on the keyboard to retain compactness. These accommodations have made it more difficult for many users to transfer their typing skills to the smaller keyboards, have increased the likelihood of user error, and have sacrificed the available options associated with the missing keys.
U.S. Pat. No. 5,141,343, incorporated herein by reference, provides an extensible and compressible keyboard by adjustable spacing between the keys using a complex mechanical assembly of folding x-shaped members which guide fixed sized keys connected by a flexible wiring circuit.
U.S. Pat. No. 5,163,765, incorporated herein by reference, provides a compressible keyboard molded from an elastomeric material which allows the space between the keys to be compressed.